Compares the keys from array against the keys from arrays and returns the difference. This function is like array_diff except the comparison is done on the keys instead of the values.
The array to compare from
Arrays to compare against
Returns an array containing all the entries from array whose keys are absent from all of the other arrays.
This function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff_key($array1, $array2);.